Portable blood glucose monitoring meters were first made available for use in the late 1970's. Portable meters provided patients and health care providers with the means to improve insulin control by permitting them to determine blood glucose levels quickly and with reasonable accuracy, without the need for vein puncture and laboratory analysis. Since the introduction of such meters, improvements to date have produced portable meters offering greater convenience in smaller sizes with more features.
Portable blood glucose monitoring meters today typically utilize disposable test strips, similar to litmus paper, that have applied chemistries that produce a color change when a drop of a patient's capillary blood is applied to the chemistries. In the case of such test strips with chemistries that produce a color change, the strip becomes darker in proportion to the amount of blood glucose present in the blood. In such cases, the strip bearing the patient's blood is inserted into the meter and the color change in the chemistry on the strip is measured using an optical reflectance system within the meter. A microprocessor-based program within the meter then processes the color change measurement and generates a digital read-out of the corresponding concentration, typically in milligrams per decaliter, of blood glucose in the patient's capillary blood. Such meters are commonly known as optical reflectance meters, and they are the most common type of portable blood glucose monitoring meter in use today.
Optical reflectance meters provide accurate results only if the test strip is inserted into the machine properly. Such optical reflectance meters also may not produce valid results if the test strip used was not designed for the meter. Previously, detection of proper test strip insertion in optical reflectance meters has been by means of a second optical channel. This greatly increases the cost of such meters and is therefore undesirable. Additionally, the second optical channel is easily corrupted by the fluid being analyzed (typically blood for consumer devices). Furthermore, an upside down strip is difficult to detect with such methods and often the primary optical channel (which is also easily corrupted by blood) has to be invoked in order to detect this condition. However, even the second optical channel method is unable to distinguish between a characterized test strip and an unknown test strip (wrong analyte, second party strip, etc). This may result in an incorrect reading being given to the user.
There is therefore a need in the blood chemistry monitoring art for a portable blood analysis system which will detect proper test strip insertion and proper test strip design prior to giving a reading to the user. The present invention is directed toward meeting this need.